Disease outbreaks have plaqued the fish industry through the years. With the growth of large scale fish culture facilities, economic losses due to disease have made their control imperative.
The world fisheries industry provides man with abundant, essential, protein-rich animal products. This harvest which is gathered by nearly all nations constitutes a basic food raw material for mankind. These commercial fisheries involve billions of dollars in the course of harvesting, processing, marketing and consumption of products. The value of the sports fishery, worldwide, is likewise substantial.
For a multitude of reasons, the commercial and sports fisheries are increasingly required to control disease problems to maintain fish populations. However, there are not presently available adequate techniques or tools for such disease control. Entire runs of fish in recent years have been substantially decimated, while others are now seriously threatened. Both hatchery and naturally propagated fish have experienced high losses, including losses to brood stocks.
Like other vertebrate animals, the young of fish are particularly susceptible to many highly infectious diseases. Obviously one cannot needle inject tiny fish on a commercial basis. A new and novel delivery system is a prerequisite to feasible drug and vaccine applications.
The problem is especially important when it is realized that serious salmon diseases may threaten the continued existence of the commercial salmon fishery as it has existed in the past. In fact, the overall future of salmon is of special concern. Today, highly prized sockeye salmon runs in California, Oregon and Washington streams appear to have been substantially damaged or destroyed. Heavy runs were recorded up to recent times. The sockeye has been the dominant economic fish species in Alaska. The Alaskan salmon pack, primarily sockeye, has in the past produced an estimated overall economic impact approaching $200 millions annually. However, recent sharp declines have been noted and fishing for this species was greatly restricted in 1974. Though the reason for these declines are varied and complex, disease is the factor which may have contributed to the recent declines.
Hatchery propagation of the sockeye species, though very desirable, has been seriously affected by one virus disease only recently identified and named. The disease is Infectious Hematopoetic Necrosis, abbreviated IHN. It is considered as one of the major causes for the damage to the sockeye runs in the Columbia river drainage system. During 1974, U.S. Fish and Wildlife Service testings indicated that IHN is widely distributed throughout Alaska in natural spawning sockeye salmon.
It is therefore highly desirable to provide an immunizing vaccine against the IHN disease. IHN is not a selective pathogen against the sockeye species. It now appears to be a serious threat to other anadromous salmonids and fresh-water trout. In the Sacramento River drainage system, salmon hatchery mortalities (in 1974) exceeded 90%; the cause is believed to be IHN. Here, the salmon species was the chinook. Of further concern is the reported indication that over 40% of the anadromous steelhead trout in this same river system carried an IHN infection.
Recently, this disease was detected in chinook returning to hatcheries in the Columbia River system. This is not really surprising since the IHN virus was prevalent in the heavy sockeye runs of the Columbia River before their substantial disappearance. If the Columbia River Chinook hatchery mortalities parallel the Sacramento River experience, this will be a problem of major regional consequences.
It is obvious, in view of the millions of dollars involved, that the West Coast states cannot afford to lose their salmon to any cause. With regard to disease, it appears now that only immunological procedures can provide the required long term, juvenile to adult, protection against viral and bacterial diseases of fish.
Various trout species have high sports and commercial value. These cold-water fish are much sought after. Infectious Pancreatic Necrosis (IPN) is one serious trout disease that significantly reduces trout populations. It is reported that the State of Oregon in both 1973 and 1974 lost much of the hatchery propagated trout stocks to this one disease.
Another viral disease is the highly infective and contagious Channel Catfish Virus Disease (CCVD). Here, the principal target market is catfish in commercial agriculture. During 1970, there were approximately 70,000 acres in catfish farm ponds in the U.S., mainly in the Southeast. Acreage planted to catfish has increased yearly the past decade. Fish are stocked at the rate of about 20,000/acre with market harvest in two years. Up to 500,000,000 fingerlings could require vaccination against CCVD annually in the U.S. There also appears to be a sizable sports propagated population of channel catfish available for vaccination.
Recognizing that there are numerous serious bacterial and fungal diseases presenting a health hazard to commercial and sports fish, it is believed that a serious need exists with respect to combating the diseases mentioned above as well as Furunculosis, caused by Aeromonas salmonicida, Vibriosis, caused by Vibrio anguillarum, and Enteric Redmouth Disease, caused by an Enterobacterium. Each disease is responsible for massive fish kills throughout the world. All salmonids would benefit from immunity to these serious bacterial diseases.